Hybrid electric single engine descent mode activation logic

ABSTRACT

Examples described herein provide a computer-implemented method that includes determining a thrust requirement to satisfy a desired glide slope. The method further includes determining, based on the thrust requirement, whether thrust matching can be maintained while operating a first gas turbine engine in a fuel-burning mode and operating a second gas turbine engine in an electrically powered mode. The method further includes, responsive to determining that thrust matching cannot be maintained, commanding fuel flow to a combustor of the second engine to cause the second gas turbine engine to operate in the fuel-burning mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 63/273,471 filed Oct. 29, 2021, the disclosure of whichis incorporated herein by reference in its entirety.

BACKGROUND

The subject matter disclosed herein generally relates to rotatingmachinery and, more particularly, to a method and an apparatus for ahybrid electric single engine descent mode activation logic.

Gas turbine engines are typically inefficient to operate at low powersettings. Operation of a gas turbine engine at idle is the typicallowest power setting available once the gas turbine engine has beenstarted. In some instances, thrust produced at idle may be greater thanthe thrust needed for ground-based operations, such as taxiing andwaiting in a parked position prior to takeoff or after landing. This canresult in excess fuel consumption and may reduce engine component lifewith many repeated taxi, takeoff, and landing cycles.

In a hybrid gas turbine engine, an electric motor can be available toassist the gas turbine engine operation by adding rotational force to aspool of the gas turbine engine while fuel flow to the gas turbineengine is reduced below idle or shut off. Such a configuration canresult in non-intuitive control from a pilot perspective, depending onhow the two energy sources, fuel and electricity, are expected to bemanaged through the range of aircraft operation. In some controlconfigurations, during operations such as engine start, thrust controlmay not be available to the pilot.

BRIEF DESCRIPTION

In another exemplary embodiment a system includes a first gas turbineengine of an aircraft, the first gas turbine engine having a first lowspeed spool, a first high speed spool, and a first combustor. The systemfurther includes a first high spool motor configured to augmentrotational power of the first high speed spool. The system furtherincludes a second gas turbine engine of an aircraft, the second gasturbine engine having a second low speed spool, a second high speedspool, and a second combustor. The system further includes a second highspool motor configured to augment rotational power of the second highspeed spool. The system further includes a controller. The controllerdetermines a thrust requirement to satisfy the desired glide slope. Thecontroller further determines whether thrust matching can be maintainedwhile operating a first gas turbine engine in a fuel-burning mode andoperating a second gas turbine engine in an electrically powered mode.Responsive to determining that thrust matching cannot be maintained, thecontroller commands fuel flow to a combustor of the second engine tocause the second gas turbine engine to operate in the fuel-burning mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that thefirst gas turbine engine provides a first thrust and that the second gasturbine engine provides a second thrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include thatdetermining whether thrust matching can be maintained includes comparingthe first thrust to the second thrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that it isdetermined that thrust matching can be maintained when the second thrustsatisfies a threshold difference relative to the first thrust

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that it isdetermined that thrust matching cannot be maintained when the secondthrust fails to satisfy a threshold difference relative to the firstthrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that thecontroller is further configured to: determine a glide range to analternate landing location; and responsive to determining that the gliderange exceeds a distance threshold, command fuel flow to a combustor ofthe second engine to cause the second gas turbine engine to operate inthe fuel-burning mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that thecontroller is further configured to track a first amount of time thesecond engine spends in the fuel-burning mode and a second amount oftime the second engine spends in the electrically powered mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include thatcommanding the fuel flow to the combustor of the second engine to causethe second gas turbine engine to operate in the fuel-burning mode isbased at least in part on at least one of the first amount of time orthe second amount of time.

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that,responsive to determining that thrust matching can be maintained, thefirst gas turbine engine continues to operate in the fuel-burning modeand the second gas turbine engine continues to operate in theelectrically powered mode

In addition to one or more of the features described herein, or as analternative, further embodiments of the system may include that thecontroller is further configured to receive the desired glide slope.

In one exemplary embodiment, a computer-implemented method for a ahybrid electric single engine descent mode activation logic is provided.The method includes determining a thrust requirement to satisfy adesired glide slope. The method further includes determining, based onthe thrust requirement, whether thrust matching can be maintained whileoperating a first gas turbine engine in a fuel-burning mode andoperating a second gas turbine engine in an electrically powered mode.The method further includes, responsive to determining that thrustmatching cannot be maintained, commanding fuel flow to a combustor ofthe second engine to cause the second gas turbine engine to operate inthe fuel-burning mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include that thefirst gas turbine engine provides a first thrust and that the second gasturbine engine provides a second thrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include thatdetermining whether thrust matching can be maintained includes comparingthe first thrust to the second thrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include that it isdetermined that thrust matching can be maintained when the second thrustsatisfies a threshold difference relative to the first thrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include that it isdetermined that thrust matching cannot be maintained when the secondthrust fails to satisfy a threshold difference relative to the firstthrust.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include determining aglide range to an alternate landing location; and responsive todetermining that the glide range exceeds a distance threshold,commanding fuel flow to a combustor of the second engine to cause thesecond gas turbine engine to operate in the fuel-burning mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include tracking afirst amount of time the second engine spends in the fuel-burning modeand a second amount of time the second engine spends in the electricallypowered mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include thatcommanding the fuel flow to the combustor of the second engine to causethe second gas turbine engine to operate in the fuel-burning mode isbased at least in part on at least one of the first amount of time orthe second amount of time.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include responsive todetermining that thrust matching can be maintained, continuing tooperate the first gas turbine engine in the fuel-burning mode andcontinuing to operate the second gas turbine engine in the electricallypowered mode.

In addition to one or more of the features described herein, or as analternative, further embodiments of the method may include receiving thedesired glide slope.

The above features and advantages, and other features and advantages, ofthe disclosure are readily apparent from the following detaileddescription when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a schematic diagram of an aircraft including dual hybridelectric propulsions systems, in accordance with an embodiment of thedisclosure;

FIG. 2 is a schematic diagram of a hybrid electric propulsion system, inaccordance with an embodiment of the disclosure;

FIG. 3 is a schematic diagram of control signal paths of a hybridelectric propulsion system, in accordance with an embodiment of thedisclosure;

FIG. 4 is a plot that graphically illustrates a relationship betweenengine spool speeds and time when transitioning through multipleoperating modes, in accordance with an embodiment of the disclosure;

FIG. 5 is a plot that graphically illustrates a relationship betweenthrust and throttle lever angle, in accordance with an embodiment of thedisclosure;

FIG. 6 is a flow chart illustrating a method, in accordance with anembodiment of the disclosure; and

FIG. 7 is a flow chart illustrating a method, in accordance with anembodiment of the disclosure.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 schematically illustrates an aircraft 10 that includes a pair ofhybrid electric propulsion systems 100A, 100B (also referred to ashybrid gas turbine engines 100A, 100B or hybrid propulsion systems 100A,100B). Each of the hybrid electric propulsion systems 100A, 100Bincludes a gas turbine engine 20 with a low speed spool 30 configured todrive rotation of a fan 42. Gas turbine engine 20 also includes a highspeed spool 32 that operates at higher speeds and pressures than the lowspeed spool 30. A low spool motor 12A is configured to augmentrotational power of the low speed spool 30. A high spool motor 12B canbe configured to augment rotational power of the high speed spool 32. Atleast one power source 16 of the aircraft 10 can provide electricalpower to the low spool motor 12A and/or to the high spool motor 12B. Thepower source 16 can be a stored energy source or a generator driven byan engine. For example, the power source 16 can include one or more of abattery, a super capacitor, an ultra capacitor, a fuel cell, a flywheel,and the like. Where the aircraft 10 includes an additional thermalengine (not depicted), such as an auxiliary power unit (APU), the powersource 16 can be a generator driven by the thermal engine. Further, agenerator of one of the hybrid electric propulsion systems 100A, 100Bcan provide power to the other hybrid electric propulsion systems 100A,100B. For example, if the hybrid electric propulsion system 100A iscombusting fuel, the hybrid electric propulsion system 100B may operatewithout burning fuel and can drive the low speed spool 30 based on thelow spool motor 12A receiving electric power from the hybrid electricpropulsion system 100A and/or the power source 16. Further, the highspeed spool 32 can be driven based on the high spool motor 12B receivingelectric power from the hybrid electric propulsion system 100A and/orthe power source 16.

While the example of FIG. 1 illustrates a simplified example of the gasturbine engine 20, it will be understood that any number of spools, andinclusion or omission of other elements and subsystems are contemplated.Further, rotor systems described herein can be used in a variety ofapplications and need not be limited to gas turbine engines for aircraftapplications. For example, rotor systems can be included in powergeneration systems, which may be ground-based as a fixed position ormobile system, and other such applications.

FIG. 2 illustrates a hybrid electric propulsion system 100 (alsoreferred to as hybrid gas turbine engine 100 or hybrid propulsion system100) as a further example of the hybrid electric propulsion system 100A,100B of FIG. 1 . In the example of FIG. 2 , the hybrid electricpropulsion system 100 includes gas turbine engine 20 operably coupled toan electrical power system 210 as part of a hybrid electric aircraft,such as aircraft 10 of FIG. 1 . One or more mechanical powertransmissions 150 (e.g., 150A, 150B) can be operably coupled between thegas turbine engine 20 and the electrical power system 210. The gasturbine engine 20 includes one or more spools, such as low speed spool30 and high speed spool 32, each with at least one compressor sectionand at least one turbine section operably coupled to a shaft (e.g., lowpressure compressor 44 and low pressure turbine 46 coupled to innershaft 40 and high pressure compressor 52 and high pressure turbine 54coupled to outer shaft 50). The electrical power system 210 can includea low spool motor 12A configured to augment rotational power of the lowspeed spool 30 and a high spool motor 12B configured to augmentrotational power of the high speed spool 32. Although two motors 12A,12B are depicted in FIG. 2 , it will be understood that there may beonly a single motor (e.g., only low spool motor 12A) or additionalmotors (not depicted). Further, the motors 12A, 12B can be electricmotors or alternate power sources may be used, such as hydraulic motors,pneumatic motors, and other such types of motors known in the art. Theelectrical power system 210 can also include a low spool generator 213Aconfigured to convert rotational power of the low speed spool 30 toelectric power and a high spool generator 213B configured to convertrotational power of the high speed spool 32 to electric power. Althoughtwo electric generators 213A, 213B (generally referred to as generators213A, 213B) are depicted in FIG. 2 , it will be understood that theremay be only a single electric generator (e.g., only electric generator213B) or additional electric generators (not depicted). In someembodiments, one or more of the motors 12A, 12B can be configured as amotor or a generator depending upon an operational mode or systemconfiguration, and thus one or more of the electric generators 213A,213B may be omitted.

In the example of FIG. 2 , the mechanical power transmission 150Aincludes a gearbox operably coupled between the inner shaft 40 and acombination of the low spool motor 12A and low spool generator 213A. Themechanical power transmission 150B can include a gearbox operablycoupled between the outer shaft 50 and a combination of the high spoolmotor 12B and high spool generator 213B. In embodiments where the motors12A, 12B are configurable between a motor and generator mode ofoperation, the mechanical power transmission 150A, 150B can include aclutch or other interfacing element(s).

The electrical power system 210 can also include motor drive electronics214A, 214B operable to condition current to the motors 12A, 12B (e.g.,DC-to-AC converters). The electrical power system 210 can also includerectifier electronics 215A, 215B operable to condition current from theelectric generators 213A, 213B (e.g., AC-to-DC converters). The motordrive electronics 214A, 214B and rectifier electronics 215A, 215B caninterface with an energy storage management system 216 that furtherinterfaces with an energy storage system 218. The energy storagemanagement system 216 can be a bi-directional DC-DC converter thatregulates voltages between energy storage system 218 and electronics214A, 214B, 215A, 215B. The energy storage system 218 can include one ormore energy storage devices, such as a battery, a super capacitor, anultra capacitor, and the like. The energy storage management system 216can facilitate various power transfers within the hybrid electricpropulsion system 100. The energy storage management system 216 may alsotransfer power to one or more electric motors on the engine, or toexternal loads 217 and receive power from one or more external powersources 219 (e.g., power source 16 of FIG. 1 , aircraft power, auxiliarypower unit power, cross-engine power, and the like).

A power conditioning unit 220 and/or other components can be powered bythe energy storage system 218. The power conditioning unit 220 candistribute electric power to support actuation and other functions ofthe gas turbine engine 20. For example, the power conditioning unit 220can power an integrated fuel control unit 222 to control fuel flow tothe gas turbine engine 20. The power conditioning unit 220 can alsopower a plurality of actuators (not depicted), such as bleed actuators,vane actuators, and the like.

One or more accessories 70 can also be driven by or otherwise interfacewith the gas turbine engine 20. Examples of accessories 70 can includeoil pumps, fuel pumps, and other such components. As one example, theaccessories 70 include an oil pump driven through gearing, such asmechanical power transmission 150B, in response to rotation of the highspeed spool 32 and/or the high spool motor 12B. Alternatively,accessories 70 can be electrically driven through power provided by theenergy storage management system 216 or other such sources of electricalpower.

Engagement and operation of the low spool motor 12A, low spool generator213A, high spool motor 12B, and high spool generator 213B can changedepending upon an operating state of the gas turbine engine 20 and anycommands received. Collectively, any effectors that can change a stateof the gas turbine engine 20 and/or the electrical power system 210 maybe referred to as hybrid electric system control effectors 240. Examplesof the hybrid electric system control effectors 240 can include themotors 12A, 12B, electric generators 213A, 213B, integrated fuel controlunit 222, and/or other elements (not depicted).

FIG. 3 is a schematic diagram of control signal paths 250 of the hybridelectric propulsion system 100 of FIG. 2 and is described with continuedreference to FIGS. 1 and 2 . A controller 256 can interface with themotor drive electronics 214A, 214B, rectifier electronics 215A, 215B,energy storage management system 216, integrated fuel control unit 222,accessories 70, and/or other components (not depicted) of the hybridelectric propulsion system 100. In embodiments, the controller 256 cancontrol and monitor for fault conditions of the gas turbine engine 20and/or the electrical power system 210. For example, the controller 256can be integrally formed or otherwise in communication with a fullauthority digital engine control (FADEC) of the gas turbine engine 20.Alternatively, the controller 256 can be an aircraft level control or bedistributed between one or more systems of the aircraft 10 of FIG. 1 .In embodiments, the controller 256 can include a processing system 260,a memory system 262, and an input/output interface 264. The controller256 can also include various operational controls, such as a hybridengine control 266 that controls the hybrid electric system controleffectors 240 further described herein, for instance, based on a thrustcommand 270. The thrust command 270 can be a throttle lever angle or acommand derived based on a throttle lever angle control of the aircraft10 of FIG. 1 .

The processing system 260 can include any type or combination of centralprocessing unit (CPU), including one or more of: a microprocessor, adigital signal processor (DSP), a microcontroller, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), or the like. The memory system 262 can store data andinstructions that are executed by the processing system 260. Inembodiments, the memory system 262 may include random access memory(RAM), read only memory (ROM), or other electronic, optical, magnetic,or any other computer readable medium onto which is stored data andalgorithms in a non-transitory form. The input/output interface 264 isconfigured to collect sensor data from the one or more system sensorsand interface with various components and subsystems, such as componentsof the motor drive electronics 214A, 214B, rectifier electronics 215A,215B, energy storage management system 216, integrated fuel control unit222, accessories 70, and/or other components (not depicted) of thehybrid electric propulsion system 100. The controller 256 provides ameans for controlling the hybrid electric system control effectors 240using a hybrid engine control 266 that can be dynamically updated duringoperation of the hybrid electric propulsion system 100. The means forcontrolling the hybrid electric system control effectors 240 can beotherwise subdivided, distributed, or combined with other controlelements.

The controller 256 with hybrid engine control 266 can apply control lawsand access/update models to determine how to control and transfer powerbetween the low speed spool 30 and high speed spool 32. For example,sensed and/or derived parameters related to speed, flow rate, pressureratios, temperature, thrust, and the like can be used to establishoperational schedules and transition limits to maintain efficientoperation of the gas turbine engine 20. For instance, a mode ofoperation of the gas turbine engine 20, such as idle, takeoff, climb,cruise, and descent can have different power settings, thrustrequirements, flow requirements, and temperature effects. The hybridengine control 266 can control electric current provided to the lowspool motor 12A and high spool motor 12B and loading effects of the lowspool generator 213A and high spool generator 213B. The hybrid enginecontrol 266 can also determine a power split between delivering fuel tothe combustor 56 and using the low spool motor 12A and/or high spoolmotor 12B to power rotation within the gas turbine engine 20.

Referring now to FIG. 4 , plot 300 graphically illustrates arelationship between engine spool speeds and time when transitioningthrough multiple operating modes. Line 302 indicates a percent speed 312of the low speed spool 30 as time 310 advances and the hybrid electricpropulsion system 100 transitions between e-taxi 306, engine start 307,and conventional idle 308. E-taxi 306 refers to a mode of operationwhere the low spool motor 12A drives rotation of the low speed spool 30to produce thrust using the fan 42, such that the aircraft 10 can bemaneuvered on the ground without burning fuel in the combustor 56. Line304 indicates a percent speed 312 of the high speed spool 32 as time 310advances and the hybrid electric propulsion system 100 transitionsbetween e-taxi 306, engine start 307, and conventional idle 308. As canbe seen in FIG. 4 , the high speed spool 32 can remain undriven duringe-taxi mode 306, which conserves energy by avoiding fuel burn and powerdraw from the high spool motor 12B. In engine start 307, the high spoolmotor 12B can be used to increase the speed of the high speed spool 32for light off and fuel burn in the combustor 56. In conventional idle308, the motors 12A, 12B may not be needed, and the gas turbine engine20 may be power by fuel burn. Alternatively, the engine-on idle statemay include a further hybrid element where the idle state of the engineincludes both fuel input and electric input to the electric motors 12A,12B, or draw through the electric generators 213A, 213B. This isreferred to as sub-idle, being possibly below conventional fuel-onlyidle in terms of either fuel flow and/or thrust.

Referring now to FIG. 5 , plot 400 graphically illustrates arelationship between thrust 412 and throttle lever angle (TLA) 410. Line402 depicts an example thrust response starting at the e-taxi mode 306of FIG. 4 , where thrust 412 can be commanded below idle by controllingthe low spool motor 12A to drive rotation of the low speed spool 30absent fuel burn in the combustor 56. Generally, the operating mode ofline 402 is for fuel off and electricity available as limited by a loweroperating limit 403. The lower operating limit 403 may be associatedwith a fuel-off detent of the TLA 410. An idle level 407 may beassociated with an idle detent of the TLA 410. Line 404 depicts anexample of a thrust response during engine start 307 of FIG. 3 , wherethrust 412 can be provided below an idle level 407 using the low spoolmotor 12A to control thrust 412 while also using the high spool motor12B to control the high speed spool 32 to provide sufficient compressionin the gas turbine engine 20 for light off in the combustor 56. Line 406depicts an example of a thrust response after starting the gas turbineengine 20 at idle level 407, such as idle 308 of FIG. 4 . Controllingthe low spool motor 12A and high spool motor 12B can support a sub-idleoperation state with thrust control at power settings lower than idlelevel 407. Thrust 12 can be controlled at a demand and power output viathe low spool motor 12A and/or high spool motor 12B for a thrust outputless than a minimum thrust output at engine idle. The thrust responsedepicted at line 406 can start at idle level 407 and continue up inrelation to TLA 410 along a response profile 408. Although lines 402,404, 406 and response profile 408 are depicted as substantially linearsegments, it will be understood that lines 402, 404, 406 and responseprofile 408 can have other shapes and characteristics.

FIG. 5 further illustrates a first region 409 where the thrust responsecharacteristic above the idle level 407 may be the same whether the fuelflow is on or off, and furthermore a second region 405 is defined belowthe idle level 407. The similar thrust response characteristic cancontinue in the second region 405 to a lower thrust level beforereaching the lower operating limit 403 at line 402. A transition fromthe lower operating limit 403 to the idle level 407 can occur duringengine start at line 404. Line 404 is an example that can shift inposition between lines 402 and 406 depending on the throttle lever angle410 position for sub-idle operation. Power provided by the low spoolmotor 12A and/or the high spool motor 12B can support engine startingbelow idle level 407 within the second region 405.

In embodiments, the controller 256 can blend the power distributionbetween the hybrid electric system control effectors 240 and fuel burnin the combustor 56. From a pilot's perspective, the setting of throttlelever angle 410 produces thrust command 270 without the pilot having todistinguish between whether motor-based thrust or fuel burn based thrustis needed. While conventional systems may use detents to prevent a pilotfrom reducing thrust 412 below the idle level 407, embodiments cansupport operation of thrust 412 down to line 402 to support e-taxi mode306 and other intermediate modes of operation below conventional idle308. Thus, control of thrust 412 can be achieved before, during, andafter engine start 307. With respect to the aircraft 10, the hybridelectric propulsion systems 100A, 100B can be independently controlledsuch that one of the hybrid electric propulsion systems 100A, 100B isoperating in a fuel burning mode while the other of the hybrid electricpropulsion systems 100A, 100B is operated using the low spool motor 12Aand/or the high spool motor 12B or a blend of fuel burn and electricpower. Such mixed modes of operation may be used, for instance, duringdescent of the aircraft 10, where thrust 412 is desired from both gasturbine engines 20, but only one of the gas turbine engines 20 activelyburns fuel. Further, embodiments can support e-taxi mode 306 with warmuptime to delay starting of the gas turbine engines 20 until reaching alocation on the taxiway away from a boarding gate.

Referring now to FIG. 6 with continued reference to FIGS. 1-5 , FIG. 6is a flow chart illustrating a method 600 for providing hybrid gasturbine engine starting control, in accordance with an embodiment. Themethod 600 may be performed, for example, by the hybrid electricpropulsion system 100 of FIG. 2 . For purposes of explanation, themethod 600 is described primarily with respect to the hybrid electricpropulsion system 100; however, it will be understood that the method600 can be performed on other configurations (not depicted).

Method 600 pertains to the controller 256 executing embedded code forthe starting and thrust control using hybrid engine control 266 alongwith other control functions. At block 602, the controller 256 canreceive a thrust command 270 for a gas turbine engine 20, where the gasturbine engine 20 includes a low speed spool 30, a high speed spool 32,and a combustor 56. The controller 256 is configured to cause fuel flowto the combustor 56 under certain operating conditions.

At block 604, the controller 256 can control a low spool motor 12A todrive rotation of the low speed spool 30 responsive to the thrustcommand 270 while the controller 256 does not command fuel flow to thecombustor 56, where the low spool motor 12A is configured to augmentrotational power of the low speed spool 30. Fuel flow can be reduced orcompletely shut off depending upon an operating state of the gas turbineengine 20. For example, the controller 256 can output a command of nofuel, fuel flow off, and/or otherwise effectively disable or reduce fuelflow as targeted. The operating state can depend on a combination ofcommands, conditions, and modes, such as an e-taxi mode, a startingmode, a ground idle mode, a takeoff mode, a climb mode, a cruise mode,an in-flight idle mode, a descent mode, a landing mode, and other suchmodes. The controller 256 can determine an allocation of the thrustcommand 270 between commanding fuel flow to the combustor 56 andelectric current to the low spool motor 12A based on the operating stateof the gas turbine engine 20 and a throttle lever angle 410, where thethrottle lever angle 410 can be received from a pilot control, anauto-pilot control, or other such source on the aircraft 10. The lowspool motor 12A can be powered by one or more of a generator, an energystorage system, and a power source 16 external to the gas turbine engine20.

At block 606, the controller 256 can control the low spool motor 12Aresponsive to the thrust command 270 during a starting operation of thegas turbine engine 20. The starting operation can be a ground-basedstart or an in-flight restart.

At block 608, the controller 256 can control the low spool motor 12A todrive rotation of the low speed spool 30 responsive to the thrustcommand at or above an idle condition of the gas turbine engine 20.

In some embodiments, a high spool motor 12B can be used in conjunctionwith the low spool motor 12A. For example, the controller 256 canreceive an engine start command 610. At block 612, the controller 256can control a high spool motor 12B to accelerate the high speed spool 32responsive to a start command while the low spool motor 12A controlsthrust of the gas turbine engine 20 on the low speed spool 30, where thehigh spool motor 12B is configured to augment rotational power of thehigh speed spool 32. Control of the high spool motor 12B of block 612can occur in parallel with control of the low spool motor 12A of block604 or blocks 604 and 612 can be other sequenced, combined, or furthersubdivided. The controller 256 can be configured to control a thrustresponse of the gas turbine engine 20 to a response profile 408 based onthe throttle lever angle 410 using any combination of the low spoolmotor 12A, high spool motor 12B, and fuel burn.

In some embodiments, a low spool generator 213A is configured to extractpower from the low speed spool 30, and a high spool generator 213B isconfigured to extract power from the high speed spool 32. The controller256 can be configured to selectively provide electrical power from thelow spool generator 213A to the high spool motor 12B and selectivelyprovide electrical power from the high spool generator 213B to the lowspool motor 12A. The controller 256 can also be configured toselectively engage either or both of the low spool generator 213A andthe high spool generator 213B to adjust a load and speed of either orboth of the low speed spool 30 and the high speed spool 32.

While the above description has described the flow process of FIG. 6 ina particular order, it should be appreciated that unless otherwisespecifically required in the attached claims that the ordering of thesteps may be varied. Also, it is clear to one of ordinary skill in theart that, the starting control described herein can be combined with andenhance other control features, such as valves, vanes, and fuel flowcontrol.

Although some embodiments described herein relate to relighting anengine during or after an e-taxi event, it should be appreciated thatthe disclosed techniques for relighting an engine can also apply toother modes of operation and/or flight phases. For example, a mode ofoperation of the gas turbine engine 20 of FIGS. 1 and 2 , such as idle,takeoff, climb, cruise, and descent can have different power settings,thrust requirements, flow requirements, and temperature effects.

An aircraft can selectively power a hybrid electric engine by providingelectric power from various sources, such as a battery system, anotherengine, and/or an APU or secondary power unit (SPU). With respect to theaircraft 10 of FIG. 1 , the hybrid electric propulsion systems 100A,100B can be independently controlled such that one of the hybridelectric propulsion systems 100A, 100B is operating in a fuel burningmode while the other of the hybrid electric propulsion systems 100A,100B is operated using the low spool motor 12A and/or the high spoolmotor 12B or a blend of fuel burn and electric power. Such mixed modesof operation may be used, for instance, during descent of the aircraft10, where thrust is desired from both gas turbine engines 20, but onlyone of the gas turbine engines 20 actively burns fuel. In such cases, itmay be desirable, during descent, to restart (e.g., relight) the one ofthe gas turbine engines 20 that is not actively burning fuel.

During descent with one of the engines 20 operating on electric powerand the other of the engines 20 operating with fuel burn, variousaspects may be considered such that the engine system operatesefficiently, and the one of the engines 20 operating on electric powercan rapidly resume a fuel-burn mode of operation (e.g., restart orrelight). However, in some cases, it may be desirable, during descent,to keep only one of the gas turbine engines 20 actively burning fuelwhile the other of the gas turbine engines 20 is operating on electricpower. The choice of whether to use only one of the gas turbine engines20 in fuel burning mode or to use both of the gas turbine engines 20 infuel burning mode can depend, for example, on the descent angle (e.g.,glide slope).

One or more embodiments described herein provides a process fordetermining when to enable a hybrid electric engine to operate in a fuelburning mode or to operate in an electrically powered mode duringdescent. For example, in some situations such as e-taxi or descent, anaircraft having two hybrid electric engines can operate with one of theengines in fuel-burning mode and the other engine operating in anelectric power (non-fuel burning) mode. This can be referred to assingle-engine descent when the aircraft is in a descent phase of flight.

During single engine descent, thrust matching is performed. For example,1000 pounds of thrust per each of the engines 20 can be achieved bydriving a fan of one of the engines 20 electrically to provide 1000pounds of thrust, and the other of the engines 20, operating in afuel-burning mode, can generate power for the electrically-operatedengine and produce 1000 pounds of thrust.

In some cases, in some cases of descent, such as with a relativelyshallower glide slope, it is more fuel efficient to operate both engines20 in the fuel-burning mode. However, in cases with a relatively steeperglide slope, it is more fuel efficient to maintain a single enginedescent (e.g., to operate only one of the engines 20 in the fuel-burningmode while the other engine 20 operates in the electrically poweredmode).

A control strategy implemented by the hybrid electric engine system canconsider a planned descent profile (e.g., a desired glide slope), abattery state of charge, and/or an estimate of transmission losses todecide whether to exercise this function of single engine descent. Otherparameters may also be considered and can include, for example, theavailability of power from an APU/SPU as a primary or backup powersource for the electrically operated engine.

With a steep approach or continuous approach, it may make more sense tooperate in single engine descent mode, which supports a steeper approachthan a traditional duel fuel-driven engine approach. Glide range toalternate landing locations may also be considered as an input toactivating single engine descent mode. For example, if the glide rangeto an alternate landing location is determined to exceed a distancethreshold, the mode of the electrically powered engine can be changed tothe fuel-burning mode. As an example, the distance threshold could bepresent, could be based on factors such as fuel burn rate, availablefuel, environmental factors, pilot input, and the like, includingcombinations thereof.

According to one or more embodiments described herein, a tradeoff ofexpected fuel savings versus component wear effects can be determinedprior to activating single engine descent mode. For example, where fuelsavings is greater than any negative effects on component wear, it maybe desirable to use single engine descent. However, where negativeeffects on component wear is greater, it may be desirable to use atraditional duel fuel-driven engine approach. Flight time with singleengine descent mode active can be tracked for each engine as well aswhether each engine operated as a fuel-driven engine or an electricallyoperated engine during single engine descent mode. This information canbe used to determine lifetime estimates for engines/components.

FIG. 7 is a flow chart illustrating a method 700, in accordance with anembodiment of the disclosure. The method 700 can be performed by anysuitable system, device, controller, etc., such as the controller 256.It should be appreciated that system, device, controller, etc., thatperforms the method can be located in a control unit of one of theengines 20, both of the engines 20, the aircraft 10, combinationsthereof, or at another location.

At block 702, a controller (e.g., the controller 256) determines athrust requirement to satisfy a desired glide slope. The desired slopecan be received, for example, from a system/controller of the aircraft,from the pilot, from a remote ground-based system, and/or the like. Thedesired glide slope indicates a desired path of descent of the aircraftpreparing to land. Some landing locations (e.g., airports) requirerelatively higher glide slopes than other landing locations due togeographic conditions, environmental conditions, local regulations, etc.Further, some aircraft operate more efficiently at certain glide slopesthan others.

At decision block 704, the controller determines, based on the thrustrequirement, whether thrust matching can be maintained while operating afirst gas turbine engine (e.g., one of the engines 20) in a fuel-burningmode and operating a second gas turbine engine (e.g., the other of theengines 20) in an electrically powered mode. As described herein, duringsingle engine descent, thrust matching is performed. For example, 1000pounds of thrust per each of the engines 20 can be achieved by driving afan of one of the engines 20 electrically to provide 1000 pounds ofthrust, and the other of the engines 20, operating in a fuel-burningmode, can generate power for the electrically-operated engine andproduce 1000 pounds of thrust. The controller determines whether thethrust matching can be maintained while the aircraft operates in singleengine descent. Determining whether thrust matching can be maintainedcan include comparing a first thrust of the first engine with a secondthrust of the second engine. It is determined that thrust matching canbe maintained when the second thrust satisfies a threshold differencerelative to the first thrust. However, it is determined that thrustmatching cannot be maintained when the second thrust fails to satisfy athreshold difference relative to the first thrust. The thresholddifference could be a percent difference between the first and secondthrusts (e.g., 2% difference), an absolute value difference between thefirst and second thrusts (e.g., 10 pounds of thrust difference), and/orthe like.

If, at decision block 704, it is determined that thrust matching cannotbe maintained, the controller, at block 706, commands fuel flow to acombustor of the second engine to cause the second gas turbine engine tooperate in the fuel-burning mode. That is, the second engine ceases tooperate in the electrically powered mode and switches to fuel-burningmode, thus providing the aircraft with dual engine descent. This ensuresthat the thrust matching can be maintained while maintaining the desiredglide slope.

If, at decision block 704, it is determined that thrust matching can bemaintained, at block 708, the first gas turbine engine continues tooperate in the fuel-burning mode and the second gas turbine enginecontinues to operate in the electrically powered mode.

Additional processes also may be included. For example, the method 700can include determining a glide range to an alternate landing locationand then, responsive to determining that the glide range exceeds adistance threshold, commanding fuel flow to a combustor of the secondengine to cause the second gas turbine engine to operate in thefuel-burning mode.

According to one or more embodiments described herein, the method 700includes tracking a first amount of time the second engine spends in thefuel-burning mode and a second amount of time the second engine spendsin the electrically powered mode. The commanding can then be based onthe first and/or second amount of time. For example, commanding the fuelflow to the combustor of the second engine to cause the second gasturbine engine to operate in the fuel-burning mode is based at least inpart on at least one of the first amount of time or the second amount oftime.

It should be understood that the process depicted in FIG. 7 representsan illustration, and that other processes may be added or existingprocesses may be removed, modified, or rearranged without departing fromthe scope of the present disclosure.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A system comprising: a first gas turbine engineof an aircraft, the first gas turbine engine comprising a first lowspeed spool, a first high speed spool, and a first combustor; a firsthigh spool motor configured to augment rotational power of the firsthigh speed spool; a second gas turbine engine of the aircraft, thesecond gas turbine engine comprising a second low speed spool, a secondhigh speed spool, and a second combustor; a second high spool motorconfigured to augment rotational power of the second high speed spool;and a controller to: determine a thrust requirement to satisfy a desiredglide slope; determine whether thrust matching between the first gasturbine engine and the second gas turbine engine can be maintained whileoperating the first gas turbine engine in a fuel-burning mode andoperating the second gas turbine engine in an electrically powered mode;and responsive to determining that thrust matching cannot be maintained,command fuel flow to the second combustor of the second gas turbineengine to cause the second gas turbine engine to operate in thefuel-burning mode.
 2. The system of claim 1, wherein the controller isfurther configured to: determine a glide range to an alternate landinglocation; and responsive to determining that the glide range exceeds adistance threshold, command fuel flow to the second combustor of thesecond gas turbine engine to cause the second gas turbine engine tooperate in the fuel-burning mode.
 3. The system of claim 1, wherein thecontroller is further configured to track a first amount of time thesecond gas turbine engine spends in the fuel-burning mode and a secondamount of time the second gas turbine engine spends in the electricallypowered mode.
 4. The system of claim 3, wherein commanding the fuel flowto the second combustor of the second gas turbine engine to cause thesecond gas turbine engine to operate in the fuel-burning mode is basedat least in part on at least one of the first amount of time or thesecond amount of time.
 5. The system of claim 1, wherein responsive todetermining that thrust matching can be maintained, the first gasturbine engine continues to operate in the fuel-burning mode and thesecond gas turbine engine continues to operate in the electricallypowered mode.
 6. The system of claim 1, wherein the controller isfurther configured to receive the desired glide slope.
 7. A methodcomprising: determining a thrust requirement to satisfy a desired glideslope; determining, based on the thrust requirement, whether thrustmatching between a first gas turbine engine and a second gas turbineengine can be maintained while operating the first gas turbine engine ina fuel-burning mode and operating the second gas turbine engine in anelectrically powered mode; and responsive to determining that thrustmatching cannot be maintained, commanding fuel flow to a combustor ofthe second gas turbine engine to cause the second gas turbine engine tooperate in the fuel-burning mode.
 8. The method of claim 7, furthercomprising: determining a glide range to an alternate landing location;and responsive to determining that the glide range exceeds a distancethreshold, commanding fuel flow to the combustor of the second gasturbine engine to cause the second gas turbine engine to operate in thefuel-burning mode.
 9. The method of claim 7, further comprising trackinga first amount of time the second gas turbine engine spends in thefuel-burning mode and a second amount of time the second gas turbineengine spends in the electrically powered mode.
 10. The method of claim9, wherein commanding the fuel flow to the combustor of the second gasturbine engine to cause the second gas turbine engine to operate in thefuel-burning mode is based at least in part on at least one of the firstamount of time or the second amount of time.
 11. The method of claim 7,further comprising, responsive to determining that thrust matching canbe maintained, continuing to operate the first gas turbine engine in thefuel-burning mode and continuing to operate the second gas turbineengine in the electrically powered mode.
 12. The method of claim 7,further comprising receiving the desired glide slope.